When modelling, when is using floating geometry acceptable or not? I have seen some artists within the industry using floating geometry, while others hard model everything into one mesh.

This has been frustrating me for a while when modelling, not being sure if I should float certain geometry or hard model it into one mesh. I'm aware the Unreal Engine prefers everything to be one mesh for lightmaps, but I have seen artists using floating geometry and having fine lightmaps.

Is it a case of using floaters for saving polys and being time efficient? Depending on the density of the mesh, if making it all into one mesh wouldn't increase the polycount dramatically?